1. Field of the Invention
This invention is related to the field of integrated circuits and, more particularly, to managing resonant frequencies on power supply inputs to the integrated circuit.
2. Description of the Related Art
As semiconductor fabrication technologies have continued to advance, larger numbers of transistors have been fabricated onto a single integrated circuit and the operating frequencies of these integrated circuits have continued to increase. Additionally, power supply voltages have decreased while power supply currents have increased in both magnitude and time variation. One effect of large, rapid swings in supply current magnitude is that resonance can be induced due to the combination of serial inductance in the package that surrounds the integrated circuit and the bypass capacitance (which can include on-die and external bypass capacitors). Resonance tends to grow and to last for long periods of time, unlike transient signals at non-resonant frequencies, which tend to die out relatively quickly.
Resonance on the supply voltage (also known as ringing) reduces the timing margin in the integrated circuit, which expects a relatively stable supply voltage. In the extreme, resonance can cause faulty operation of the integrated circuit.
One way that resonance has been limited or avoided in the past is to increase the serial resistance in the package to damp the resonance. However, such techniques have a practical limit. The IR drop in the package is increased by increasing the serial resistance, thus reducing the effective operating voltage that the integrated circuit itself experiences for a given externally-supplied voltage and for a given current. Furthermore, increasing the serial resistance increases the power consumption of the package itself, which can be problematic if the integrated circuit is a high power consumer or if the integrated circuit is designed for power-conscious applications such as battery-powered devices or devices with limited cooling capabilities.